On a carbon dioxide gradient in the Fucales egg

Citation

Abstract

Previous investigations suggest that a CO2-pH gradient is involved in the development of polarity in the Fucales egg. To test this hypothesis, a method was developed to measure the relative CO2 output from the two hemispheres of this egg. The eggs are photosynthetically tagged with C14 and embedded in a thin jelly membrane in which the eggs develop. One measures separately the respiratory C14O2 emitted from the two surfaces of the membrane during each of a series of intervals before, during, and after the eggs are unilaterally illuminated to orient their future axes. New methods are described for obtaining eggs, for controlling and measuring the thicknesses of egg-bearing jelly membranes, and for measuring C14O2. Because of a drop in the specific radioactivity of the emitted carbon dioxide, the sum of the rates of respiratory C14O2 emission from the two faces of a membrane decreases rapidly with time; but the C14O2-ratio, or the ratio of the rates of C14O2 emission from the two faces, changes very slightly with time. That face which had been lower while the membrane gelled nearly always emits C14O2 more rapidly than the other face. This is attributed partly to a settling of the eggs in the membrane while it gelled and partly to a higher respiratory rate somehow induced in the hemispheres of the eggs which point toward the formerly lower face. These "lower" hemispheres also tend to become the rhizoid poles. The changes of the C14O2-ratios with time are attributed primarily to changes in the relative specific radioactivities in the carbon dioxide emitted from the two hemispheres of the eggs, rather than to further changes in the relative respiratory rates of these hemispheres with time.